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Error: 7161 The mass matrix is zero - resolve

March 12, 2013, 6:59 am
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Respected sir/ma'am,

I am trying to simulate a Nano ElectroMechanical Switch(NEMS) using the following modules:a)solid, stress-strain, b) Moving Mesh, and c)Electrostatics.
When i run the solver, it shows an error message:'Error: 7161 The mass matrix is zero' along with a warning: 'Not all domains are meshed'.
The sizes are in nano domain. Model is attached for your kind reference.
For meshing i used Mapped Meshing to reduce number of elements.
I am using Version 3.5a on Pentium processor with 32 bit and 2 GB RAM.

Thank You in advance
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failed to evaluate variables

March 12, 2013, 7:51 am
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Hi ,

I am building a 3d model of fluid flowing around a wafer using 4.3a. The following error occured when I tried to plot the pressure on the edge of the wafer.




Cannot ecaluate expression.

Failed to evaluate variable.
- Variable: mod1.p
- Geometry: 1
- Domain: 5

Failed to evaluate expression.
- Expression: mod1. p
- plot: lngr3(line graph)

Domain 5 is the wafer in my geometry. Can anybody help me out please?
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different physics with different meshes in 3D

March 12, 2013, 8:44 am
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Hello,

I work on a casting model with a phase change in a metallurgy process.
The 2D-axy model works fine and i begin the 3D model.
I work on a 3D coupled problem with different physics: mf for excitation, ht and spf. ht and spf are strongly coupled.
To achieve the solution of my model i have to compute something like this:

stationary solver
step1:mf
step2:ht1
step3:spf1
step4:ht2
step5:spf2
...
step10:spf10

After this sequence i reach the solution of the 2D-axy model.

The problem is that my mf.Qh source term for electromagnetic heating (ht) and Lorentz force (spf) is increasing after each step! I think that problem is linked to mesh density.
I use a specific mesh for mf and ht (dense) and spf (light). spf can not be meshed as fine as ht and mf because of memory issue.
What can i do to avoided the increase of source term? What kind of solver should i use preferentialy?
Thank you for your help

Julien
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Electric field between electrodes

March 12, 2013, 9:51 am
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Hello

I am trying to make a very simple model to calculate electric field between two electrodes in water facing each other(using electrostatics module). I set for the electrode boundaries opposite electric potentials, however when I compute the result that I am getting looks very counter-intuitive, as the field lines are coming out from only the corners and there is no linear field lines between electrodes. I am quite new so there might be boundary conditions missing. Any ideas?
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Avoiding Negative Concentrations

March 12, 2013, 12:16 pm
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Hello,

I would like to make sure that my reaction rate is such that when the concentration of the species approaches zero, then so does the species sink.
Comsol Says:
This can be achieved for instance by writing max(eps^2,Q). eps is an internal COMSOL constant that is a very small number in the order or 10-15. This type of expression is also good if you want to avoid Q being 0.

Where would you write max(esp^2,Q) ?
In the reaction term? Defining your concentration as a variable?

Thank you,
Kelley
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modeling nanostructured organic solar cell with Comsol

January 2, 2011, 1:47 am
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Hi,how can I modeling Zinc oxide nanostructures organic solar cell in which include the effects of optical interference, exciton diffusion, charge separation via the formation of polaron pairs, and charge transport in two separate interpenetrating phases with Comsol? Thanks alot!
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Piezoresistive modeling

May 29, 2012, 8:26 am
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Hello all

I want to simulate a piezoresistive beam with Comsol.
I was looking to find an example of piezoresistive modeling to find out what module they usually use and how are the settings but i didn't find any
It seems there was an example of "piezoresistive elevator button" before for old version of Comsol. But it is not avail;able anymore.
Can anyone send me this example or any other helpful link about piezoresistive simulation by Comsol?

Best
Bahar

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Problem about Joule heating and thermal expansion

September 22, 2012, 5:22 am
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Hi

I want to inject ac current (amplitude is fixed) to a silicon beam and hope to see maximum expansion when the ac frequency is at half of the mechanical resonant frequency of the beam. I tried using "Joule heating and thermal expansion" physics and frequency domain solver in Comsol 4.2 but the result is the same to the case where no current is applied. Reasonable result can be obtained when using stationary solver. Does anyone know how to solve this? Thanks.
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Mie scattering in 4.3

January 7, 2013, 4:44 am
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Hello,
I have already seen some discussion about mid scattering of a gold nanosphere. But I the discussions I have consulted, no one has yet implemented a mie scattering program in Comsol 4.2 or 4.3 that works as the one in 3.5. Has this problem been solved yet? Can anyone post the correct program here?
Thank you very much for the help
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New "Introduction to COMSOL Multiphysics" book now available

February 5, 2013, 1:42 pm
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Hello,

We are pleased to announce that a new version of the "Introduction to COMSOL Multiphysics" book is now available for immediate download at:
www.comsol.com/shared/download...uctionToCOMSOLMultiphysics.pdf

The highlights of this new version are:
- a brand new introduction chapter
- a thorough overview of the COMSOL Desktop
- updated models with step-by-step instructions
- new appendices about shortcuts, language elements and reserved names, file formats and LiveLink add-ons

Enjoy!
Valerio
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Electrical resistance in a structure

March 11, 2013, 3:39 am
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hello everybody,
I need to have a simulation of electrical potential in 1D beam elements in a structure. I want to give potential to one point of the model and ground to another point and observe the current flow inside the beam. in fact I need to calculate the whole electrical resistance inthe structure.
when I use Electrical Current in AC/DC module, it tells me that it is not applicable to select a point as a "point electric potential" or "point ground".
I have attached a picture of a sample structure.
How can I do this. should I use another module?

Thanks in advance
Ehsan
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Problem in my Results

March 11, 2013, 3:17 pm
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Hello everyone,

I'm having a problem simulating a cylinder of copper. The surround of it is a cube with PML and scattering condition.
But my results (attached) seems a little strange. Can anyone help me?

Thanks.

Gustavo
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Output pressure of the transducer in frequency domain

March 12, 2013, 12:23 am
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Hello,everyone
I'm doing research in capacitive ultrasonic transducer. I use the electromechanic model and want to observe the output pressure in the frequency domain. Now I can add the biased voltage which contains both Vdc and Vac. But it's in the time domain. But it can't run in the frequency domain. Could anyone tell me how to make it in the frequency domain please? Thank you!
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Simulation of leakage flux from transformer

March 12, 2013, 9:31 pm
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Hello.

I've tried to simulate a quantity of leakage flux from transformer by using COMSOL 4.3a. To do this, I made a simple transformer model with LiveLink for AutoCAD.(I want to attach mph file, but its size is too big to attach)
And I chose "mef" module for simulation. But an error message comes out. Here is the message.

The following feature has encountered a problem:

Failed to find a solution.
Divergence of the linear iterations.
Returned solution is not converged.
- Feature: Stationary Solver 1 (sol1/s1)
- Error: Failed to find a solution.

I'm a beginner of COMSOL, so I can't find any solutions to fix this error. Is there any way to fix this error?

Regards,

Mizuki
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bistatic radar cross section

March 12, 2013, 9:37 pm
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Hello!

I studied the given tutorial related to radar cross section.

Unfortunately, these only provides how to plot monostatic RCS.

I tried to use parametric sweep, but it wasn't successful.

Can I get a clue in drawing bistatic RCS?

I desperately need your help.
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Magntic field analyses using current excitation

March 13, 2013, 10:29 am
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Hello,
I have started to use Comsol this week and have done some examples, but when I try to simulate my
model I hit some set backs.

The model has 16 electromagnetic poles with a pair of coils in quadrature wound on silicon steel.
So I have 32 coils each 90 turns.

I need to do the following:
1) Import the steel BH curve into Comsol for the Silicon Steel
2) Excite the coils using currents modeled by the following equations i.e.
ix = Ip*(cos(phi*pi/180)*cos(2*pi*freq*t)-r*sin(phi*pi/180)*sin(2*pi*freq*t));
iy = Ip*( sin(phi*pi/180)*cos(2*pi*freq*t)+r*cos(phi*pi/180)*sin(2*pi*freq*t));
Ip is the magnitude of the current phasor and r, freq are constants.
3) So should I choose stationary or time dependent for the study for the magnetic field physics?
4) Choose a method or physics for exciting the coils - is it Electrical Circuit(cir) or Magnetic Fields(mf)
5)The other question is how do I set the depth of my model

Generally my problem is similar to an assembly of inductors which produce flux similar to
a magnetic Halbach array.

Find the geometry attached (orange colored regions are coils, the grey regions are the
iron cored parts, the faint purplish color is defined as air).

I was able to import a 2D dxf file and I can also add the materials
(a) How can I view the domains and do I need to split the geometry to parts so that I can associate parts of the same material?

Regards and I hope you will assist me since am in the introductory stage.

Wanjiku
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AC/DC training courses in Phoenix, AZ and Burlington, MA

March 13, 2013, 12:43 pm
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An invitation is open for our Discussion Forum readers! You are invited to attend one of our upcoming AC/DC focused training courses that will take place within the next few weeks. The first course will be offered in Phoenix, AZ on March 21st. The second will be offered in Burlington, MA on April 11th. Join us in learning how to use the AC/DC Module for modeling steady-state, transient, and low frequency electromagnetic phenomena relevant for modeling of resistors, capacitors, inductors and coils, motors, magnets, and electromagnetic heating.

Phoenix, AZ - March 21
comsol.com/c/mgt

Burlington, MA - April 11
comsol.com/c/mgv

We hope to see you there!

Best regards,
Kristen O'Connor
Marketing Assistant
COMSOL, Inc.
kristeno@comsol.com
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Tightly folded Inflatable structure deployment simulation possible in comsol ?

March 13, 2013, 9:12 pm
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Hi,

We have a problem where we need to simulate the deployment of a tightly folded inflatable structure. I have used explicit ALE method in a different software to achieve this, however it takes a long time to solve as the simulation time is 4 seconds. And I need to use a finer mesh but that would reduce my timestep and time to solve would be unrealistic.

I believe one solution is to switch to an implicit solver. Can comsol handle such a problem ? From my experience it needs to handle non-linear contacts, fluid - structure interaction and large deformations of the fabric.

Any info would be appreciated.

Thanks,
Shiva
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Temperature effect in Electrostatic module.

March 14, 2013, 12:15 am
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Hi,

I am using Comsol ver 3.5a. Can anyone guide me that how could i observe the effect of temperature on capacitance value in Electrostatic module ? From where i can change/control the temperature in Electrostatic module ?

As i am working on 12 electrode capacitance sensor filled with oil and would like to observe the change in capacitance values based on temperature change.

Please guide me.

Thanks.

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Gaussian heat flux

March 14, 2013, 1:13 am
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I want to use Gaussian heat flux in Comsol 4.3.
1.As given in this module we are using function gp1 but what is the position and standard deviation values for it.
2. Is it necessary to have axi-symmetric body for the Gaussian pulse.
3. Because we have the equation for Gaussian pulse with 'r' and 'R' terms, we know 'R' but what is 'r' in this and if we wish to use 2D non axi-symmetric geometry then how to use 'r' value in that.
4. If we are using inbuilt Gaussian pulse function then tell us, how to find the standard deviation and how to define position

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